1. Field of the Invention
This invention relates to a method for making foamed articles having a laminated structure which are used as a cushion for automotive sheets and in which foamed layers of different physical properties are integrally combined.
2. Description of the Prior Art
For the satisfaction of a requirement for improving automobiles with respect to the comfort, there has been proposed a seat cushion having a soft foamed layer on one side which contacts the human body and a rigid foamed layer on the opposite side. The seat using this type of cushion is soft to the surface touch and becomes hard as one sits down, ensuring comfort and stability.
The cushion has been made by several methods including a method in which a soft foam and a rigid foam are separately formed or cut and are bonded togther by means of an adhesive, and a method in which a separately formed first layer is set in a mold and a second layer is superimposed on the first layer. However, these method are disadvantageous in that the productivity is low with increasing production costs and when the adhesive is used, the bonded portion becomes hard, so that one will feel a physical disorder when sitting.
Japanese Patent Application Laid-open Nos. 55-96195 and 59-138423 have proposed methods which can cope with the above problems. These methods comprise, as shown in FIGS. 24 to 26, pouring into a mold 1 a first foamable liquid composition 2 (hereinafter referred simply as first composition) and then a second foamble liquid composition 3 (hereinafter referred to simply as second composition) on the first composition 2 at the time when the first composition 2 is foaming. In this method, the second composition 3 passes through the first composition 2, which is in the course of foaming and has thus a lowered specific density, to the bottom of the mold where it foams.
Since, however, the second composition 3 is poured over the first composition 2 which is foaming, the second composition 3 entrains and mixes with the foaming first composition 2 at the pouring portion A. Accordingly, the resultant product has a mixed layer of a foamed layer 2 of the first composition 2 and a foamed layer 3 of the second composition 3 at the pouring portion A as particularly shown in FIG. 27. The cushion obtained by this method inconveniently gives, more or less, a feeling of physical disorder because the resiliency at the pouring portion A is different from that at the other portions.
Moreover, it is difficult for the second composition 3 poured through the first composition 2 being foamed to spread at the bottom of the mold 1, so that the foamed layer formed from the second composition tends to become thick at the pouring portion A and thinner at a more distant place, resulting in a non-uniform thickness, as shown in FIG. 27. Thus, there is a demand for a cushion which is comfortable to sit down on.
Also, in the above method, the second composition which has been poured into the first composition is compressed by application of foaming pressure of the first composition, so that the foamed layer of the second composition is liable to become harder than desired.